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Switch-to-lookup tables: Don't require a result for the default
case when the lookup table doesn't have any holes. This means we can build a lookup table for switches like this: switch (x) { case 0: return 1; case 1: return 2; case 2: return 3; case 3: return 4; default: exit(1); } The default case doesn't yield a constant result here, but that doesn't matter, since a default result is only necessary for filling holes in the lookup table, and this table doesn't have any holes. This makes us transform 505 more switches in a clang bootstrap, and shaves 164 KB off the resulting clang binary. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199025 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -3428,7 +3428,7 @@ GetCaseResults(SwitchInst *SI,
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Res.push_back(std::make_pair(PHI, ConstVal));
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}
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return true;
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return Res.size() > 0;
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}
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namespace {
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@ -3499,12 +3499,14 @@ SwitchLookupTable::SwitchLookupTable(Module &M,
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// If all values in the table are equal, this is that value.
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SingleValue = Values.begin()->second;
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Type *ValueType = Values.begin()->second->getType();
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// Build up the table contents.
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SmallVector<Constant*, 64> TableContents(TableSize);
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for (size_t I = 0, E = Values.size(); I != E; ++I) {
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ConstantInt *CaseVal = Values[I].first;
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Constant *CaseRes = Values[I].second;
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assert(CaseRes->getType() == DefaultValue->getType());
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assert(CaseRes->getType() == ValueType);
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uint64_t Idx = (CaseVal->getValue() - Offset->getValue())
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.getLimitedValue();
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@ -3516,6 +3518,8 @@ SwitchLookupTable::SwitchLookupTable(Module &M,
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// Fill in any holes in the table with the default result.
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if (Values.size() < TableSize) {
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assert(DefaultValue && "Need a default value to fill the lookup table holes.");
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assert(DefaultValue->getType() == ValueType);
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for (uint64_t I = 0; I < TableSize; ++I) {
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if (!TableContents[I])
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TableContents[I] = DefaultValue;
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@ -3533,8 +3537,8 @@ SwitchLookupTable::SwitchLookupTable(Module &M,
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}
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// If the type is integer and the table fits in a register, build a bitmap.
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if (WouldFitInRegister(TD, TableSize, DefaultValue->getType())) {
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IntegerType *IT = cast<IntegerType>(DefaultValue->getType());
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if (WouldFitInRegister(TD, TableSize, ValueType)) {
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IntegerType *IT = cast<IntegerType>(ValueType);
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APInt TableInt(TableSize * IT->getBitWidth(), 0);
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for (uint64_t I = TableSize; I > 0; --I) {
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TableInt <<= IT->getBitWidth();
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@ -3552,7 +3556,7 @@ SwitchLookupTable::SwitchLookupTable(Module &M,
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}
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// Store the table in an array.
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ArrayType *ArrayTy = ArrayType::get(DefaultValue->getType(), TableSize);
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ArrayType *ArrayTy = ArrayType::get(ValueType, TableSize);
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Constant *Initializer = ConstantArray::get(ArrayTy, TableContents);
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Array = new GlobalVariable(M, ArrayTy, /*constant=*/ true,
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@ -3723,20 +3727,29 @@ static bool SwitchToLookupTable(SwitchInst *SI,
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}
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}
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// Get the resulting values for the default case.
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// Keep track of the result types.
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for (size_t I = 0, E = PHIs.size(); I != E; ++I) {
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PHINode *PHI = PHIs[I];
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ResultTypes[PHI] = ResultLists[PHI][0].second->getType();
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}
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uint64_t NumResults = ResultLists[PHIs[0]].size();
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APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
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uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
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bool TableHasHoles = (NumResults < TableSize);
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// If the table has holes, we need a constant result for the default case.
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SmallVector<std::pair<PHINode*, Constant*>, 4> DefaultResultsList;
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if (!GetCaseResults(SI, 0, SI->getDefaultDest(), &CommonDest,
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if (TableHasHoles && !GetCaseResults(SI, 0, SI->getDefaultDest(), &CommonDest,
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DefaultResultsList, TD))
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return false;
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for (size_t I = 0, E = DefaultResultsList.size(); I != E; ++I) {
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PHINode *PHI = DefaultResultsList[I].first;
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Constant *Result = DefaultResultsList[I].second;
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DefaultResults[PHI] = Result;
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ResultTypes[PHI] = Result->getType();
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}
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APInt RangeSpread = MaxCaseVal->getValue() - MinCaseVal->getValue();
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uint64_t TableSize = RangeSpread.getLimitedValue() + 1;
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if (!ShouldBuildLookupTable(SI, TableSize, TTI, TD, ResultTypes))
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return false;
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@ -806,3 +806,53 @@ return:
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; CHECK-NOT: @switch.table
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; CHECK: switch i32 %c
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}
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; If we can build a lookup table without any holes, we don't need a default result.
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declare void @exit(i32)
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define i32 @nodefaultnoholes(i32 %c) {
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entry:
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switch i32 %c, label %sw.default [
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i32 0, label %return
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i32 1, label %sw.bb1
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i32 2, label %sw.bb2
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i32 3, label %sw.bb3
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]
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sw.bb1: br label %return
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sw.bb2: br label %return
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sw.bb3: br label %return
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sw.default: call void @exit(i32 1)
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unreachable
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return:
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%x = phi i32 [ -1, %sw.bb3 ], [ 0, %sw.bb2 ], [ 123, %sw.bb1 ], [ 55, %entry ]
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ret i32 %x
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; CHECK-LABEL: @nodefaultnoholes(
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; CHECK: @switch.table
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; CHECK-NOT: switch i32
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}
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; This lookup table will have holes, so we cannot build it without default result.
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define i32 @nodefaultwithholes(i32 %c) {
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entry:
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switch i32 %c, label %sw.default [
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i32 0, label %return
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i32 1, label %sw.bb1
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i32 2, label %sw.bb2
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i32 3, label %sw.bb3
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i32 5, label %sw.bb3
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]
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sw.bb1: br label %return
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sw.bb2: br label %return
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sw.bb3: br label %return
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sw.default: call void @exit(i32 1)
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unreachable
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return:
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%x = phi i32 [ -1, %sw.bb3 ], [ 0, %sw.bb2 ], [ 123, %sw.bb1 ], [ 55, %entry ]
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ret i32 %x
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; CHECK-LABEL: @nodefaultwithholes(
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; CHECK-NOT: @switch.table
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; CHECK: switch i32
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}
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